Toggling a GPIO pin at 50 + MHz

[con3]

Posted on November 06, 2017 at 16:22The original post was too long to process during our migration. Please click on the attachment to read the original post.

[Tesla DeLorean]

Posted on November 07, 2017 at 14:15

Signal looks awful, try putting scope probe in 10x mode.

[Tesla DeLorean]

Posted on November 07, 2017 at 14:17

Check optimization level on compiler. Consider using pointer.

What toolchain?

[waclawek.jan · Accepted solution]

Posted on November 07, 2017 at 14:22

Looks very much like you're hitting the limits of your measurement setup, i.e. scope bandwidth and (more probably) probe bandwidth - unless there's some limitation imposed by the PCB and/or connected circuitry, too.

Is it a 1:10 probe?

Also, from which memory are you running? Did you confirm your system clock runs at the frequency you assume it does?

JW

[waclawek.jan]

Posted on November 07, 2017 at 14:23

Clive One wrote:

Check optimization level on compiler. Consider using pointer.

What toolchain?

The best thing to find out whether this is the issue is to see the disasm.

JW

[con3]

Posted on November 07, 2017 at 14:37

Completely agree, I'll see if I can find some that have higher limits, It's a 1:10 Probe (60 MHz) and a TDS3014C 100 MHz oscilloscope. Measuring directly onto the pins on the dev board at this point. 

I checked the system clock, outputted a prescaler onto the RCC_MCO_2 and it was definitely at 216 MHz.

[con3]

Posted on November 07, 2017 at 14:40

I'm running atollics truestudio with the following: 

[con3]

Posted on November 07, 2017 at 14:40

I implemented it with a 10x probe, didn't look any better, I might be hitting the probe limits, I'll try and get a higher bandwidth probe

[con3]

Posted on November 07, 2017 at 15:38

This completely solves it, I thought the probe was 100 MHz as well until you pointed it out. Got a higher MHz probe and just measured a 109 MHz signal.

Thank you for all the help.

Sometimes its not the mcu but rather how we're trying to observe the mcu.

[con3]

Posted on November 07, 2017 at 16:27

[LMI2]

Posted on November 07, 2017 at 16:46

Something is still too slow. If you want to see 50MHz square wave correctly you need to have 3*50MHz and 5*50MHz or more harmonics too.